1. Field of Invention
The present invention relates to the devices and systems used to open and close a valve coupled, either directly or via an intermediate spool, to a vessel, which may contain a fluid, distillate, or unconsolidated debris byproduct produced from a manufacturing process, such as the several types of coke produced from a petroleum refinery process, as well as to the several methods employed for unheading a vessel utilizing such devices or systems. Specifically, the present invention relates to a valve actuator system comprising an actuator, a gear box assembly, and a transmission assembly, the transmission assembly designed to open and close a deheading valve attached to a coke drum to facilitate the removal of coke during the decoking process.
2. Background
Electric actuators mount on valves which, in response to a signal, move the valve to a desired position using an outside power source. Various electric types of motors use AC or DC electricity to drive a combination of gears to generate the desired torque level. There are various types of electric actuators used in different industries depending on a desired application. Each type of actuator may be used with a specialized valve of choice. For example, rotary electric actuators are typically used in combination with a ball, plug, and butterfly valves. Linear electric actuators are often used with a gate, globe, diaphragm, pinch, and angle valves that feature a sliding stem that opens or closes the valve. Electric actuators often provide control and indexing capabilities to allow multiple position stops along strokes.
In the hydrocarbon processing industry, many refineries recover valuable products from the heavy residual oil that remains after refining operations are completed. This recovery process is known as delayed coking and produces valuable distillates and coke in large vessels or coke drums.
When a coke drum is full it must be emptied of the byproduct it holds in preparation for refilling the coke drum in another cycle. First, the coke drum is steam purged and cooled with quench water. The coke drum is then drained of water and vented to atmospheric pressure, after which the top and bottom flanges are removed, a process referred to as de-heading. Once the coke drum is de-headed, the coke remaining within the coke drum is removed and emptied into a catch basin. Once the coke is removed, the heads are replaced and the coke drum is prepared to repeat the cycle.
In addition to the dangers inherit in the unheading of a coke drum during the decoking process, space on the working deck around the deheader valve is limited. Various prior art devices have been utilized as deheader valves. Electric actuator systems, pneumatic actuator systems and hydraulic actuator systems have all been utilized in prior art deheader valve systems. In typical electric actuator systems, the drive stem extends beyond the electric actuator when the blind is in an open position, such that use of an electric actuator requires an additional several feet of deck space during operation. Additionally, prior art electric actuators allow tortional loads to reach the valve stem, resulting in increased wear on system elements within the valve itself. Wear within the valve necessitates expensive downtime and repair. The large amount of floor space required to accommodate these assemblies and devices that automate removal of the flange head from the coke drum is extremely undesirable and downtime of the valve is profoundly expensive for a decoker operation.
Additionally prior art electric actuators have unpredictable life spans. The pressure, load and velocity at which electric actuators most move a gate through the open and closed positions affect where on the actuator system wear will occur. Side loading, the cut of threads, dirt and other debris additionally affect prior art devices and can accelerate wear and decrease the life of the actuator. Additionally, prior art devices have failed to produce electric actuators which produce constant thrust output for a constant torque input. Accordingly, prior art actuators produce inconsistent thrust output over the lifespan of the electric actuator producing inconsistent and undesirable results. Further prior art systems utilizing electric actuators often fail to open and close quickly enough to mitigate dangerous conditions inherent in unheading a coke drum during a de-coking process. Such prior art devices are not capable of operating within the size constraints imposed by the environment at the bottom of a coke drum, are incapable of producing consistent thrust output over the lifespan of the actuator and do not allow for predictive maintenance and can produce unsafe conditions.